Plant pests are a major factor in the loss of the world's important agricultural crops. About $8 billion are lost every year in the U.S. alone due to infestations of non-mammalian pests including insects. In addition to losses in field crops, insect pests are also a burden to vegetable and fruit growers, to producers of ornamental flowers, and to home gardeners.
Insect pests are mainly controlled by intensive applications of chemical pesticides, which are active through inhibition of insect growth, prevention of insect feeding or reproduction, or cause death. Good insect control can thus be reached, but these chemicals can sometimes also affect other, beneficial insects. Another problem resulting from the wide use of chemical pesticides is the appearance of resistant insect varieties. This has been partially alleviated by various resistance management practices, but there is an increasing need for alternative pest control agents. Biological pest control agents, such as Bacillus thuringiensis strains expressing pesticidal toxins like δ-endotoxins, have also been applied to crop plants with satisfactory results, offering an alternative or compliment to chemical pesticides. The genes coding for some of these δ-endotoxins have been isolated and their expression in heterologous hosts have been shown to provide another tool for the control of economically important insect pests. In particular, the expression of insecticidal toxins in transgenic plants, such as Bacillus thuringiensis δ-endotoxins, has provided efficient protection against selected insect pests, and transgenic plants expressing such toxins have been commercialized, allowing farmers to reduce applications of chemical insect control agents.
Other, non-endotoxin genes and the proteins they encode have now been identified. U.S. Pat. Nos. 5,877,012, 6,107,279, 6,137,033, and 6,291,156, as well as Estruch et al. (1996, Proc. Natl. Acad. Sci. 93:5389-5394) and Yu et al. (1997, Appl. Environ. Microbiol. 63:532-536), all herein incorporated by reference, describe a new class of insecticidal proteins called Vip3. Vip3 coding sequences encode approximately 88 kDa proteins that are produced and secreted by Bacillus during its vegetative stages of growth (vegetative insecticidal proteins, VIP). The Vip3A protein possesses insecticidal activity against a wide spectrum of lepidopteran pests, including, but not limited to, black cutworm (BCW, Agrotis ipsilon), fall armyworm (FAW, Spodoptera frugiperda), tobacco budworm (TBW, Heliothis virescens), and corn earworm (CEW, Helicoverpa zea). More recently, plants expressing the Vip3A protein have been found to be resistant to feeding damage caused by hemipteran insect pests. Thus, the Vip3A protein displays a unique spectrum of insecticidal activities. Other disclosures, WO 98/18932, WO 98/33991, WO 98/00546, and WO 99/57282, have also now identified homologues of the Vip3 class of proteins.
The continued use of chemical and biological control methods heightens the chance for insects to develop resistance to such control measures. Also, only a few specific insect pests are controllable with current measures.
Therefore, there remains a need to discover new and effective pest control agents that provide an economic benefit to farmers and that are environmentally acceptable. Particularly needed are control agents that are targeted to a wider spectrum of economically important insect pests and that efficiently control insect strains that are or could become resistant to existing insect control agents. Furthermore, agents whose application minimizes the burden on the environment are desirable.